Power reverse gear



y 27, 1941' E. M. SHANNON I 2,243,656

POWER REVERSE GEAR Filed April 14, 1957, 5 Sheets- Shet 1 REVERSE CUTOFF INVNTOR l ELLwoon M. Sunuuou l 145 A ORNEY y 1941- E. M. SHANNON I2,243,656

POWER REVERSE GEAR Filed April 14, 1937 5 Sheets-Sheet 2 INVENTORELLwoon l1. finnunon ATTORNEY May E E. M. SIHANNON 2,243,653

POWER REVERSE GEAR 6 Filed April 14, 1937 5 Shets-Sheet 3 Fig. 6

, INVENTOR ELLWOOD N. SHANNON AE Z ORNEY;

May 27 1941. E. M. sHANNoN POWER REVERSE GEAR Filed April 14, 1937 [gasI 5 Sheets-Sheet 4 Patented May 27, 1941 rowan REVERSE-GEAR Ellwood M.Shannon,- Bala Cynwyd, Pa.

Application 'April 14, 1937, Serial No. 136,772

10 Claims.

This invention relates generally to power reverse gears for locomotivesand more particularly to an improved screw type power reverse gear.

Innumerable types and arrangements of power reverse gears have beenproposed or used in the past fifty years or so, but notwithstanding thisgreat amount, of efl'ort there are noticeable defects in these priordesigns from the standpoint of construction, operation or maintenance.As

. to the operation, the principal problem has to do with prevention ofcreeping. In some instances, it has been proposed to overcome creepingin fluid actuated types of power reverse gears by mechanically lockingthe piston rod. This involves complications and uncertainties ofcontrol, and to overcome these the screw type power reverse gear hasbeen proposed and used, the screw inherently tending to provide alocking action. However, the screw type power reverse gears have notbeen entirely satisfactory because of insuflicient or complicatedcushioning means and also because such gears have structuralcomplications as well as not having suflicient sensitivity and fastoperation under certain conditions. Nevertheless the screw type offerscertain desirable characteristics.

It is an object of my invention to provide an improved screw type powerreverse gear that has the desirable characteristics of this general typea of gear but without-the objectionable characteristics thereof.

Another object is to provide improved resilient means in a simple,compact and inexpensive manner for cushioning the forces transmittedfrom the locomotive valve gear to the screw.

A further object is to provide an improved combination in a screw typepower reverse gear whereby various operating parts such as theservomotor, screw, crosshead, resilient means and reduction gearing maybe effectively encased within a housing containing a substantial amountof oil for lubricating said parts as well as others.

It is also an object of my invention to provide improved control meanswhereby the screw mechanism and parts connected thereto are brought to agradual and easy stop at the extreme limits of travel.

A still further object is to provide an improved brake mechanism for theservo-motor and screw together with an improved control apparatustherefor whereby the servo-motor may operate freelywhen actuating thescrew and yet on completion of the operation of the motor is effectivelyheld in position.

Another object is to provide an improved arrangement whereby the cut-offindicator may be located in the cab in asimple and eifective manner.

An additional and very desirable object is to accomplish the foregoingobjects in a structure that is simple, compact and inexpensive inconstruction, operation and maintenance and yet is highly rugged andpositive without sacrifice of sensitivity or accuracy together withhaving the various parts readily accessible for inspection or repair.

Other objects and advantages will be more apparent to those skilled inthe art from the following description of the accompanying drawings inwhich:

Fig. 1 is a fragmentary diagrammatic side elevation of a locomotiveshowing the general application of my improved power reverse gear and rcontrol, the usual valve gear being omitted for sake of clarity;

Fig. 2 is a front elevation of the cut-off indicator;

Fig. 3 is a transverse sectiontaken on the line 3-8 of Fig. 2;

' Fig. 4 is a plan view of the power reverse gear proper with partsbroken away to show certain parts in detail;

Fig. 5 is a longitudinal vertical section through v the power reversegear proper taken substantially on the line 5-5 of Figs. 4 and 6;

Fig. 5a is a transverse section taken on the line 5a5a of Fig. 5;

Fig. 6 is'a transverse sectionthrough the servo motor takensubstantially onthe line 6-6 of Fig. 7 is a horizontal sectiontakensubstantially on the lines 1-1 of Figs. 5 and 6 to show the distributingvalves of the servo-motor;

Fig. 8 is a vertical transverse section taken substantially on the line8-8 of Figsrl, 9 and 10, showing the main control handles for both theair operated servo-motor and braking mechanism together with the brakecontrol exhaust valve;

Fig. 9 is a' vertical section taken on the line 99 of Fig. 8 to show theforward and reverse main control valves;

. Fig. 10 is a horizontal section taken on the line III-ill of Fig. 8;'

Fig. 11 is a plan view of the inner end of the l2--|2 of Fig. 13 to showthe brake operating pistons and cylinders in cross-section and isfurther broken away to show an additional valve forreleasing fluidpressure from the brake cylinders wh'en itis desired to make a manuallycontrolled precision adjustment of the cute-off;

Fig. 13 is a vertical longitudinal section .through the brake mechanismand the manually operable precision adjusting means;

Fig. 14 is a horizontal section taken on the line I4-l4 of Fig. 12showing two of the brake pistons and cylinders.

The invention, such as is specifically disclosed herein merely for thepurpose of illustrating one specific form among possible others that theinvention might take in practice, comprises essentially four coordinatedmechanisms, namely, the power reverse gear proper including the screwand servo-motor with the various improved features thereof, the maincontrol valve mechanism normally located in the cab and adapted toeffect forward or reverse operation of the servo-motor, the brakingmechanism and its control for positively holding the servo-motor andscrew in any desired fixed position, and the precision adjustingmechanism.

'Power reverse gear proper.This, as generally indicated at I, Fig. 1, ismounted in any suitable manner on the locomotive to adjust any usual andwell-known valve gear not shown. The reverse gear includes (Figs. 4 and5) a stationary crosshead guide housing 2 in the form of a cylinderhaving side brackets 2 for attachment to the locomotive. A hollow rod 4extending through a packing 6 in a reduced neck portion 2 of the housinghas a usual head 1 adapted for pivotal connection to a reach rod la fortransmitting longitudinal adjusting movement to the usual valve gear. Acollar 2 is threadedly secured to the inner end of rod 4 and a.cylindrical pistonlike crosshead 9 slidably supported in cylinder 2 isthreadedly connected to collar 2. The integral piston-like crosshead 9and rod 4 are hereinafter referred to as a piston and piston rod. Ascrew l0, journalled in a partition I l at one end of housing 2, extendswithin hollow rod 4 and carries a cooperating threaded nut l2. This nuthas a threaded, or otherwise suitably formed, flange l2 at one end andthe other end has, Fig. 5a., a series of alternate radial recesses andlugs l4. These lugs are axially slidably received in suitable radialrecesses l5 formed in collar 2, lugs I! being formed alternately withsaid recesses.

in radial alignment with. and axially slidable within, flange I2 is aflange l1 projecting inwardly from piston 9. These two sets of flangesand lugs, constitute radially aligned laterally extending surfaces.Washers l2 and I! are normally held in seating engagement respectivelywith flanges l2 and I1 and lugs l4 and It by a single interposed coilspring 20. Appreciable relative axial movement can occur between nut I2and piston 9 by reason of recesses l5 extending from the left side ofcollar 2 inwardly to an annular groove 2| therein although the extent ofsuch relative movement is limited by the spacing between the successivecoils of the spring.

The motive power and gear connections for actuating the screw It maycomprise any suitable or standard form of fluid operated servo-motor andgears, which however are herein p ovided with improved end plates andheads having a novel structural and functional cooperation with theremaining elements. The motor specifically disclosed herein and as shownparticularly in Fig.

6 is of the radial blade-piston type having a rotor 22 journalledeccentrically in a motor housing 22. The rotor has a shaft 24, Fig. 5.connected through a pinion 25 and gear 22 to rotate screw it. Thehousing 22 is connected to cylinder 2 by a bolted offset gear housing 21forming an end closure for the cylinder. Otherwise the specific detailedconstruction of the motor per se does not constitute a part of mypresent invention except in the manner in which its operation iscoordinated with movement of piston 2 at the extremes of its travel.

The distributing valve mechanism forthe servo-motor includes as shown inFig. 7 two opposed pressure fiuid inlets 20 and 2! adapted to bealternatively connected respectively by a suitable shuttle valve 22 toinlet passages 22 and 24. As shown in Fig. 6, the passages 22 and 24connect into side chambers 25 and 22, and these chambers in turn areadapted to be alternatively connected through a port 21 of a rotatablesleeve 2| with their respective passages 22 and 24, thereby to entirelyshut of! supply of pressure air to the motor, or the ports 42 and 4| maybe alternatively opened. The transverse movement of shuttle valve 22 iscoordinated with the oscillatable movement of sleeve valve 22 by acylindrical pin 42 projecting eceentrically therefrom into a recess 44in the side of valve 22 whereby axial movement of valve 22 will impartrotation to valve 22. In one position of valves 22 and 22 such as shownin Figs. 6 and 7, the servo-motor will rotate in one direction and inthe other extreme position of said valves opposite rotation will result,while an intermediate position of said valves will cause said motortostop.

To coordinate movement of piston 2 with the distributing valve mechanismjust described; a limit rod 44, Fig. 4, is slidably supported at 44 and41 by the cylinder heads. This rod is pivotally connected through a link42 and arm 42 to a vertical segmental pinion shaft 52, Figs. 4 and '7,this pinion. meshing with a rack ll formed on the side or shuttle valve22. Rod 42 also carries a pair of limit or stop'lugs 52 and 22 suitablyadjustably secured to the rod, convenient access to these limit lugsbeing had by removal of either one or both of a pair of cover plates 22.The pision 2 is adapted to engage these lugs in approaching either ofthe extreme limits of travel, thereby to operate pinion shaft 52 andrack ii to return shuttle valve 22 to its neutral position. In thismanner, the motor cannot jam the piston I and nut l2 at either end ofits extreme positions. To render this limit stop apparatus compact, arecess 22 is formed in the left end of piston 2. Fig. 4, to receive stop52 which is hereby adapted to bemoved to its maximum rearmost positionas shown in dotted lines at 52 while permitting piston 2 to extend stillfurther to the left. The housing I- and the various parts as constructedare conducive to maintaining a high level of lubricant within thehousing, this lubricant then circulating, Fig. 5', through ports 6| tothe screw while as shown in Fig. 4 the right end of shaft 42 has freecommunication through a passage 22 within the cylinder housing.

Braking mechanism.-To prevent rotation of the screw through vibration,the outwardly extending rotor shaft 62 is flexibly connected throughjointed shafts 64 to a shaft 45, Fig. 13,

.3 operating fluid from main supply chamber 8|,

of a brake mechanism located in the cab. A brake disc 81, keyed at 88 toshaft 85, has an annular recess in which an annular brake shoe 58 isdisposed. This brake shoe is brought into frictional engagement withbrake disc 81 by a plurality of brake pistons 88, I8, II and I2, Figs.12 and 14, disposed in cylindrical bores of a brake housing I3. Cupwasher packings are held against the pistons, Fig. 14, by springs I4.The pistons are held in position during assembling of 10 the brake by apair of vertical pins I5 and I8, Figs. 12 and 14, extending downwardlythrough casing I3 and elongated slots such as 11 formed in the ends ofthe pistons. Small compression springs 18, Fig. 14, are interposedbetween rods I5 and I8 and the piston to move the pistons away from thebrake disc 88 when air pressure is exhausted. The spr ngs I8 are ofsuiiicient strength to overcome springs I4 so as to move pistons. and I2to the right when air pressure is released from behind the pistons. Aseries of pins I8, Fig. 13, are secured in casing I3 and project intosuitable radial slots I8 of brake shoe 88 thereby to prevent it fromrotating with brake disc 81 upon engagement therewith. 2

Main control valve mechanism.To control supply of operating fluid toservo-motor 23 and to control the engagement or disengagement of thebrake elements 81 and 88, a valve housing 88, Figs. 8, 9 and 10, has amain chamber 8| to which pressure fluid from any suitable source issupplied through an inlet-82. An outlet chamber 83 communicates througha pipe 84 with. shuttle valve inlet 38, Fig. 7, while an outlet chamber85, Fig. 10, communicates through a pipe 88 with the other shuttle valveinlet 3I. Communication between chambers 8|, 83 and 85 is controlled bya pair of main control valves 88 .and 88 normally urged downwardly bysuitably adjustable spring pressed slidable collars 88 and 8|, thevalves being bodily removable through enlarged openings closed bythreaded plugs-.82. The valves have downwardly projecting stems 83and83a suitably guided in arms 84. The valves are alternately raised byrotation of a handle 85 secured to a shaft 86, Fig. 8, which has abevelled sealing contact 81 with a suitable projection on casing 88.Formed integrally with or otherwise suitably secured to said shaft aretwo pairs of oppositely extending fingers 88 and 88, Fig. 11, adaptedrespectively to engage the under side of collars 88 and 8|. Both valves,however, are adapted to be in closed position when handle 85 is in itsneutral position. By raising say valve 88, fluid pressure is suppliedfrom chamber 8I to pipe 84, Figs. 9 and 7, thereby shifting shuttlevalve 32 to open port 48 and simultaneously cause sleeve valve 38 torotate. Pressure fluid is thus admitted to cause rotation of theservo-motor and screw I8 in one direction. When valve 88 is opened andvalve 88 closed, fluid pressure is admitted to pipe 88 to shift shuttlevalve 32 so as to open port 4| and rotate sleeve valve 38 in theopposite direction, thereby to operate the servo-motor and screw I8 inthe opposite direction. When both valves 88 and 88 are closed, theservo-motor is prevented from rotating by virtue of brake shoe 88 beingpressed against brake disc 81, Figs. 13 and 14, now about to bedescribed.

Brake control valve mechanism.'1o control the operation of the brakeshoe 88 by pistons 88-'I2 in cooperation with the operation of main.control valves 88 and 88, I continuously supply Fig. 9, downwardlythrough; a port I8I into a horizontal passage I82, Figs. 9 and 10,thence through an adjustable needle controlled orifice I83 to an exhaustvalve chamber I84 from which a passage I85 extending vertically downwardfor communication with a continuing passage I85a, Figs. 12, 13 and 14 inthe brake housing I3. The control valve housing 88 is suitably securedto a supporting flange I 88 of housing I3. Passage I85a first suppliesfluid pressure to pistons 58 and I8 through a passage I81 and thence byvertical passage I88 and I88 to the lower pistons which in turn areconnected by a cross-passage I I8.

To exhaust air from the brake cylinders and thereby release the brake topermit rapid unrestricted rotation of the servo-motor 23, I provide,Fig. 8, an exhaust valve II3 normally yieldingly held to its seat butadapted when opened to discharge fluid from chamber I84 throughatmospheric ports II4, Fig. 8. This valve is operated by a finger leverII5 pivotally mounted at IIG on a suitable projection of handle 85whereby handles 85 and H5 may ,be simultanemovement of handle to eitherits forward or reverse position will immediately operate control valves88 and 88, Fig. 9, to cause rotation of the servo-motor. Conversely whenthe handle II5 released, exhaust valve II3, Fig. 8, is closed therebycausing pressure to build up behind the brake pistons to apply brakingaction to the servomotor through disc 67, shaft 65 and the jointedconnecting shafts 84. When the handle 5 is in neutral, the valveoperating end II5a, Figs. 8 and 10, is positioned in a recess I I5b,thereby preventing operation of the servo-motor without first releasingthe brake. To release the brake, le-

' ver I I5a is moved into a laterally enlarged recess 50 and upon handle85 thereafter'being rotated away from its neutral position to operatethe servo-motor, then lever II5a will be laterally moved and accordinglybe held in its releasing position by one or the other of walls 5d. Hencethe supply of operating fluid to the servomotor must be shut off beforethe brake can be applied.

Precision adjusting mechanism.-To effect precision adjustment of thepower reverse screw I8, I have provided improved means for releasing thebraking action and thereafter effecting manual rotation of the screw.This precision mechanism as shown in Fig. 13 comprises a hand wheel I28journalled on the outer end of shaft 85 and held in position by asuitable cover I2I which is removably secured to casing I3 by bolts I22.The hubof this hand wheel has straight faced clutch teeth I23 adaptedwhen moved inwardly to engage complementary clutch teeth I24 formed onthe hub of brake disc 81. An axially shiftable pin I25 extends throughshaft 85 for abutting engagement with handle I28 while .its other endengages a compression spring I26. Shaft 65 is provided with a slot I21through which.

, supported by easing flange I3, washer ary brake control exhaust valveI3I which is normally yieldingly urged to its closed position by aspring and also by fluid pressure in crosspassage IIO, Figs. 12 and 13.The valve I3I when opened allows cross-passage H and the otherintercommunicating air supply passages I03 and I09, Fig. 12, to beconnected to exhaust passages I32, Fig. 13.

A finger latch I35, Fig. 13, normally engages clutch teeth I23 toprevent inward movement of hand wheel I20, but upon pulling out of latchI35 hand wheel I may be pushed inwardly which not only engages teeth I23and I24 but also pushes pin I25 inwardly together with cam sleeve I29,thereby forcing valve I3I downwardly to exhaust the fluid pressureacting on the brake pistons. Thereupon rotation of hand wheel I20 willcause rotation of brake disc 01 and shaft 85 through key 65, thereby torotate the jointed shaft 64 and servo-motor rotor 22 and thence screw I0to effect a final precision adjustment of the cut-off.

To determine the position of the servo-motor, I have provided as shownin Figs. 2, 3 and 13 an improved dial and operating means comprising acasing I40 having a. cylindrical opening I in which a bushing I42 isdisposed, this bushing having a pinion and shaft I43 eccentricallydisposed therein for engagement with a pointer driving gear I44. Pinionshaft I43 is connected by a flexible shaftI45 to worm gear I46, Fig. 13.This gear meshes with suitable threads I41 formed on the periphery ofshaft 55. A suitable lamp I48 is I40 to suitably illuminate theindicating hand I49. Suitable graduations I50 indicate the per cent ofcut-off in either forward or reverse direction as well as the neutralposition. In case the power reverse gear is of such a type that thereverse and forward positions are contrariwise to those disclosed in thespecific embodiment, it isoniy necessary to move eccentric shaft housingI42, Fig. 3, downwardly to disengage gear I44 and then rotate supportI42 through 180 so that the box can then engage the other side of gearI44 as shown in dotted lines at I5I.

Operation To move the power reverse piston 4 in one direction, brakerelease handle II5, Fig. 8, is

'manually squeezed against main control handle 95, thereby opening valveII3, Fig. 8, so as to connect ports I05 and I05a, Figs. 8, 12 and 13, toatmospheric exhaust ports Hi4. Brake pistons 59-42, Figs. 12 and 14,thereby relieve their holding force on the brake shoe 68 which normallyacts'against the brake disc 51. The operator now swings handle 95' sothat shaft 96 and, say fingers 99, Fig. 9, engage collar 6| to raisevalve 98 whereupon fluid pressure supplied from a suitable sourcethrough inlet 82 and chamber BI is conducted through pipe 94 to inlet30, Fig. 7, thereby shifting shuttle valve 32 to admit fluid pressurethrough port 40 and passage 33 to rotate radial vane type rotor 22. Thisrotation is transmitted, Fig. 5, through gears 25 and 26 to rotate screwI0 and accordingly axially move nut I2. The nut transmits its motionsuccessively through I0, spring 20, washer I9 and lugs I6 to piston rod4. Or, if the nut is moved in the opposite direction upon reverserotation of the screw, then its motion is transmitted successivelythrough lug I4, washer I9, spring 20 and flange H to the piston rod 4.It is also seen that any vibrational forces transmitted from thelocomotive valve gear to piston rod 4 will be cushioned by the action ofthe spring, washers,- flanges or lugs just described. Rotation of motorshaft 63, Fig. 5, transmits its motion through a jointed shaft 64, Fig.1, to the braking shaft 55, Fig. 13, and thence through gears I40 andI41 to flexible cable I45, Fig. 3. This cable actuates pointer I49 andwhen it reaches any predetermined cut-off, the engineman then returnshandle 95, Figs. 8 and 9, to its neutral position to close valve 80. Theservo-motor rotor 22, Fig. 6,

thereupon stops. Simultaneously with the return' of handle 95 to itsneutral position the lower end II5a of brake control handle II5 movesout into the recess I I5b to permit closure of exhaust valve II3, Fig.8. Thereupon fluid pressure is conducted from chamber 8|, Fig. 9,through port IOI to passage I02, Fig. 10, and thence through the orificeI03, controlled by adjustable needle valve I03a, to chamber I04 andpassages I05 and I050. to move the brake pistons 69-42 and brake shoe 68against brake disc 61 which is keyed at 55 to shaft 95. This shaftbyvirtue of the jointed shafts 64 and rotor shaft 03 positively stopsrotation of the rotor and screw and also prevents gradual shifting of.nut I2 along the screw by reason of vibration transmitted thereto.

To effect operation of the power reverse gear in the opposite direction,handle 95 is swung so as to cause fingers 90 to open valve 89, whereuponfluid pressure is conducted from the main supply chamber 5| to chamber85 and thence through pipe 85, Fig. 10, to inlet 3I, Fig. 7, to

- shift shuttle valve 32 to uncover port H and close port 40, the fluidpressure then being supplied through passage 34 and 36, Fig. 6, torotate servo-motor rotor 22 in the opposite direction. Simultaneouslysleeve valve 38 is rotated by shuttle valve 32 through the pin andslotconnection 43, 44, Fig. "I, so as to connect exhaust port 31, Fig.6, with passage 35.

To effect precision adjustment of the power reverse gear, the enginemanafter releasing a catch I35 merely moves hand wheel I20 axiallyinwardly, Fig. 13, which through pins I25 and I20 causes cam I30 to opensupplementary brake control exhaust valve I3I, thereby exhaustingpressure fluid from the brake piston cylinders as through cross-passageIIO, Figs. 12 and 13, past valve I3I to atmospheric passages I32.Simultaneously with axial movement of cam I30, clutch teeth I23 and I24are brought into engagement whereby manual rotation of hand wheel I20will then rotate shaft 05 through key 55 and accordingly rotate thejointed shaft-04, rotor shaft 33 and the servo-motor gearing togetherwith screw I0. This will effect manual movement of nut I2 and piston rod4 so long as hand wheel- I20 is rotated. When the desired degree ofprecision adjustment has been effected, the engineman merely pullsouthand wheel I20, Fig. 13, to permit closure of valve I3I whereupon theconstant supply of brake actuating pressure through port I0 I Fig. 9,will apply a braking action to shaft 55.

To insure maximum safety in the movement of mechanism not being appliedunless the engineman returns handle 95 to neutral. In the oppositedirection of movement of piston 9, Fig. 4 it will engage a stop lug 53to shift rod 45 to the right, thereby reversely actuating shuttle valve32 so as to cover both ports 40 and 4| to stop the servo-motor.

From the foregoing disclosure it is seen that I have provided a highlyeffective power reverse gear that is positive in operation and yet hasmaximum flexibility and responsiveness with minimum effort on the partof the engineman. This is accomplished with minimum possibility ofcreeping and yet vibrational forces from the valve gear are adequatelycushioned in a relatively simple; compact and efficient device employingonly a single spring that functions for vibratory movement in eitherdirection. The precision ad Justment of the cut-off position may beobtained without undue restraint by the major control parts, thisprecision adjustment being accomplished in a simple and yet highlycoordinated manner with the major control elements. It is also seen thatprovision is made for continuous lubrication in a common casing for thescrew,

nut, reduction gears 25 and 26 and servo-motor rotor parts and valveswith minimum possibility of the lubricant draining therefrom.

It will of course be understood that various changes in details ofconstruction and arrangement of parts may be made by those skilled inthe art without departing from the spirit of the invention as set forthin the appended claims.

I claim:

1. A power reverse gear comprising, in combination, a rod, a screw,means including a nut operatively connecting said screw and rod, arotatable servo-motor for operating said screw,

' means for commonly supporting the rod, the "screw and the servo-motor,a plurality of cooperating valves for controlling and distributing.

operating fluid to said servo-motor, including a shuttle valveselectively disposable in forward, neutral or reverse position, andmeans including a shiftable link and a rotatable element actuatedthereby so as to move said shuttle valve to its neutral position andthereby shut down said motor automatically when said rod has moved to apredetermined position in its travel.

2. A power reverse gear comprising, in combination, a rod, a screw,means including a nut operatively connecting said screw and rod, arotatable servo-motor for operating said screw, means for commonlysupporting the rod, the screw and the servo-motor, a'plurality of c0-operating valves for controlling and distributing operating fluid tosaid servo-motor, and means for operating one of said valves so as toshut down said motor automatically when said rod has moved to apredetermined position in its travel, said valve which is automaticallycontrolled by movement of said rod comprising a shuttle valve to whichfluid pressure is alternatively supplied at two inlets with connectingports betweensaid inlets and said motor, said valve and ports beingarranged so that in the extreme positions of the shuttle valve, one orthe other of said ports is open and in the neutral position both of saidports are closed, whereby V admission of fluid pressure to one of saidinlets causes one of said ports to be opened and admission of fluidpressure to the other inlet causes the other port to be opened, andmeans operatively connected to said rod for moving said shuttle valve toits neutral position automatically in accordance with a predeterminedmovement of said rod.

3. A power reverse gear comprising, in combination, a screw and nut, arotatable servomotor for effecting relative rotation between said screwand nut a housing located alongside of the locomotive boiler forcommonly supporting the nut, the screw and servo-motor, a control valvemechanism located in the locomotive cab at a point remote from saidservo-motor for controlling supply of operating fluid thereto,relatively rotatable braking elements located in the cab, a rotatableshaft connected to said servomotor and extending therefrom to said cabfor connection to the rotatable braking element, and means located insaid cab for releasably controlling the braking mechanism therein.

4. The combination set forth in claim 3 further characterized in thatsaid releasable braking means includes a pair of frictionallycooperating relatively rotatable braking elements one of which isradially supported by the other.

5. A powerreverse gear comprising, in compressure of said frictionalbraking means to allow said supplemental operating means to be actuated.

6. A power reverse gear comprising, in combination, a rod, a screw,means including a nut for operatively connecting said rod and screw, arotatable servo-motor for effecting relative rotation between said screwand nut, releasable braking mean operative to restrain rotation betweensaid screw and nut, supplemental means for effecting said relativerotation between said nut and screw, and means controlled by saidsupplemental operating means thereby to release said braking meansautomatically upon initial actuation of said supplemental means.

7. The combination set forth in claim 6 further characterized by theprovision of means whereby said braking means is applied automaticallyupon discontinuance of the actuation of said supplemental operatingmeans.

8. The combination set forth in claim 6 further characterized in thatsaid releasable braking means includes a pair of frictionallycooperating relatively rotatable braking elements one of which isradially supported by the other, said means which is controlled by saidsupplemental'means including a valve operating rod extending coaxiallythrough said braking elements and one end of said rod having engagementwith said supplemental means and the other end of said rod having valveactuating means adapted to release said braking means upon axialmovement of said rod.

-' means having mechanical clutch elements adapted to be releasablyenaaged upon axial movement of said supplemental means, and said meansfor releasing the braking means includes a rod movable axially throughsaid friction elements and engageable at one end with said supplementalmeans and having connection at its other end with a tapered sleeveencircling said shaft, and a valve laterally operable by said taperedsleeve for controlling the release of said braking means.

10. A power reverse gear comprising, in combination, a rod; a screw,means including a nut for operatively connecting said screw and rod, 9.

rotatable servo-motor for eilecting relative rota- ELLWOOD M. SHANNON.

